Focal length question

[Chris Arthur]

In trying to define a camera intrinsic, there are parameters for focal length and for initial focal length.  How to choose initial focal length?  I have a theory below, but can somebody verify it?

I got an old canon rebel camera used off of ebay along with a lens (18 to 55mm).  Without using zoom the focal length is 18mm.  That should go into the camera intrinsic as the focal length.   In the viewfinder, the camera will also give a focal length distance, As an approximate distance to the subject from camera.  Suppose that the camera reads this as seventy five centimeters, is this what counts as the initial focal length in meshroom?  Does this focal length distance matter at all?